Screw piles are metal pipes hollow inside, at the end of which a blade is welded that performs the function of a drill. Such a support with a screw tip is responsible for transferring the load from the house, which provokes its weight, to the ground. Due to the characteristic anchor structure, the foundation element is firmly fixed in the ground and is not pushed up due to heaving during freezing of the soil.
Destination
Such a development appeared by chance, because everyone knows that winter lightning is a serious problem for lightweight structures, especially when it comes to building a wooden house on watery clay soil. Even deepening the support below the freezing line may not give the desired result, since the low weight of the building does not counteract the significant heaving forces acting on the lower base segment, and it is fully or partially pushed up. And only thanks to the expansion that screw piles of the screw type are equipped with, such troubles can be avoided.
A dense layer of soil holds the blade securely, and the metal pin remains in place. Here you do not have to worry about pile breaking, since tensile strength characteristics of steel correspond to 330 - 600 MPa, while the heaving forces do not exceed 0.2 MPa.
Typical supports, their diameter and weight
The dimensions of the piles and their length must correspond to the category of the structure. Typical sizes of cone supports involved in private construction have the following parameters:
- CB89x250;
- CB108x300;
- CB133x350.
The first numerical value indicates the diameter of the stem (mm), and the second the diameter of the helical blade. For structures with light weight, which include fences and garden buildings, a support with a barrel diameter of 76 mm is suitable. A fence with brick pillars, country outbuildings, hinged structures and arbors are installed on cones with a diameter of 89 mm. For a small wooden house made of timber and logs, as well as frame buildings, galvanized blade rods of a slightly larger size (108 mm) are suitable. Well, the most powerful samples of the bearing elements of the foundation (133 mm) complete our rating, more than withstanding the onslaught of a heavy log cabin and foam block construction. In order to accurately calculate the size of the necessary piles with a tip, you need to know at least the approximate weight of the future choir.
Advantages
Screw piles are actively used in private construction. Such a foundation with or without concrete grillage is excellent for erecting low-rise buildings. It can withstand the weight of a small brick or wooden house, utility structures made of foam concrete and frame outbuildings without any problems. The base with metal supports is easy to install, reliable and affordable. But most importantly, the structure can be mounted on complex soils with different terrain at any time of the year and in any weather.. The eco-foundation does not require cutting down vegetation and it is not necessary to carry out vertical planning of the site for it. It is worth noting that in some cases screw piles for the foundation are the only and irreplaceable solution.
Disadvantages
Despite the many advantages, such supports still have disadvantages, and in the first place it is a lesser resource than concrete elements of a similar purpose. This disadvantage is caused by the fact that metal supports are susceptible to corrosion caused by soil moisture. In addition, you can often encounter frankly low-quality goods produced by an unscrupulous manufacturer, and no one is safe from this. Savings in materials, the use of welding, the absence of anti-corrosion treatment lead to the fact that such an important bearing element quickly collapses.
How long the pipes can serve depends on the grade and thickness of the metal, the degree of processing and composition of the anticorrosion agent, the quality of the weld in the places of welding, the composition and water saturation of the soil. You can choose a really high-quality product guided by the accompanying documents:
- certificates
- passports
- production test protocols.
Incorrect operation, incorrectly selected diameter of supports, incorrectly calculated building weight or installation errors reduce the product life by several years. For example, you simultaneously use metal piles as supports and an earthing switch, but in the event of a breakdown of the neutral conductor and current leakage through the steel cone, the corrosion process will increase many times, and this will primarily happen in the weld area. If there are electrical substations, cellular repeaters, railroad tracks near the site, in a fifty-meter zone, and the soil contains a large amount of moisture, the pile-screw foundation will be constantly exposed to harmful effects (stray currents, ground vibrations).
Types of Blade Piles
There are two types of screw piles: welded and cast galvanized screw type, and they are separated depending on the method of integration of the tip.
Weld tip
In the first case, we are dealing with an economy option made of a pipe and a helical blade welded to it. Often, such products are of poor quality, as they can easily be made in the artisanal way, respectively, and the price is suspiciously low. It is these types of screw piles that cause a lot of dissatisfied reviews, which is not surprising, because they spoil the eco-foundation from concrete and serve little.
The slightest error during the welding of the blade and pipe will lead to the fact that during screwing in dense soil the pile deviates from the vertical. In the worst case, screw-type blade products are torn in place of the weld. Naturally, the stability of the house will be violated and sooner or later it will skew or sag.
With manual twisting, you will clearly feel the separation: the supporting element will turn with particular ease, but will not go into the ground. It is much more dangerous that a low-grade support will deform in a similar way over time due to rust or damage to the seam. After the gap between the pipe and the tip, the entire load will unevenly transfer to neighboring piles, which will cause subsidence under the grillage, and the house will become emergency.
If you already use cheap specimens with a welded tip, then only for the installation of fences and temporary shelters.
Starting the construction of a house, for your own benefit, ask the contractor what supports, cast or welded, he uses in his work.
Cast tip
Cast galvanized tips are made using special technology of high-quality steel, due to which the construction of the pile is one-piece. The body of such supports are galvanized pipes with a welded steel tip. Blade elements of this type, the pipe diameter of which is 108 mm, the length is 2.5 m, and the metal thickness corresponds to 4 mm, have a weight of 35 kg with a bearing capacity of up to 6 tons. Their solid cast tips have a base thickness of 13 mm (diameter 300 mm, unlike welded ones - 5 mm) and are distinguished by geometric accuracy. Cast galvanized screw piles for concrete are more expensive than welded ones by a quarter, which is explained by greater reliability and much better quality indicators.
If you want to choose a truly reliable support, pay attention to the cast galvanized products, in which the barrel is coated with a polymer composition. Here, the tip does not have to be treated with anticorrosion, since due to friction against the soil when screwing in, the polymer can wear off to the metal base itself, and the dense layers of the soil practically do not contain oxygen, so you can not worry about corrosion for many years.
Steel screw piles of a screw type, reinforced with a cast tip, are reliable, they are smoothly and easily immersed in complex fine-rocky soil, and the eco-foundation with their use will serve as a durable and high-quality support for construction for more than a decade. Experts note that with proper installation and proper operation, a concrete foundation, the weight of which rests on reinforced cones, can stand for more than a century.
Buying galvanized screw piles of a screw type with solid cast tips, also do not lose vigilance, because now fakes and marriage literally flooded the construction market. Violation of the factory process, the lack of post-heat treatment, the use of low-grade steel or an unstable pipe diameter will lead to disastrous consequences, so again we recall the documents that must be checked, because by acquiring a defective product, you risk a lot, including health.
Even a well-filled concrete foundation made of concrete will not support the weight of the house if the supports are defective. In no case do not ignore the special equipment that controls the power moment of screwing, and also bother after installation to test the screw piles under pressure in accordance with all the rules in compliance with the technology.
Finally, I would like to note thick-walled piles created on the basis of a tubing. They can compete with products with a cast tip. The characteristic of their quality is high, which indicates reliability and durability. The barrel of such a support has a thickness of up to 7.5 mm - similar pipes are widely used in the gas industry, because they are absolutely not subject to corrosion and have a huge resource.
Now that we have examined the popular types of screw piles that support concrete, their standard length is known, the weight they can withstand, it remains to calculate their number and choose a diameter in accordance with the future construction, after which we can proceed with construction.